That doesn't look like blur, but a kicked tripod or a stacking-software error. Each of your stacked exposures are relatively crisp. The stack is just not aligning obvious features properly.

If you are using software that is trying to align a bracket set, it must be getting confused with the willow branches swaying in the breeze. I would use a manual alignment of the frames, using features that don't move (the ring of bricks around the lawn, or house corners).